Illuminating system for projecting motion pictures in color



Oct. 8, l RA THOMAS ILLUMINATING SYSTEM FOR 4PROJECTING MOTION PICTURESIN COLOR Filed July 9, 1934 SP M/ Qg Rza/mrd T g @el am.

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rfmnmd Patented Oct. 8, 1935 UNITED STATES ILLUMINATING SYSTEM FORPROJECTING MOTION PICTURES 1N COLOR Richard Thomas, Los Angeles, Calif.,assignor of one-half to William Jennings Bryan, Jr., Los

Angeles, Calif.

application July s, 1934, serial No. 134,360

1 claim. (ci. sii- 16.0

This invention relates to the ari; of projecting colored photographicimages and relates particularly to that system of additive color inwhich multiple images of different color values are sil multaneouslyprojected in super-imposed relation upon a screen and there coloredlight corresponding to the color values of each positive image is l insuperimposed relationship, and `further pro-v vides means for changingthe color characteristics of the projected light by means of colornlters to correspond with the color values of the frames in projection.

Customarily the color values upon one of the two frames is registeredupon the film by the exposure oi' that frame through a red illter andthe color values registered upon that frame are the red color values inthe objective field. In like manner, the color value images upon theother of the two frames is registered upon the film by the exposure ofthat frame through a green illter and the color values registered uponthat frame are the green color values in the objective eid. When such afilm is projected in such a projector system and the light passingthrough the red color value frame is likewise projected through a redillter andthe green color value image is simultaneously projectedthrough a green filter, and the resultant red and green images aresuper-imposed to form a single composite image upon the screen, suchcomposite image is neither red nor green but is portrayed in the naturalcolor effect.

In such a system I have found that it is essen- .tial for the productionof natural color over the entire area of the screen image that the lightintensity be equal upon all parts of the screen image. In order toattain this result, I have found it necessary to develop an entirely newtechnique in the art of screen illumination through a projector. It hasbeen necessary to ,o change radically the conception of the functionsent principles and technique involved in the two systems. .v

Let us consider rst the projection of a single picture area. In suchcase the light from any given light source is passed through lenticularIl condenser-s and through a single aperture plate of a size tocorrespond with the size of-the iilm area used. The lm image is thusprojected through the projector lens to the screen stationed before theprojector. 'I'he purpose of the conl0 denser in such a system is togather the maximum light rays from the light source and to condense theminto an area which at the aperture plate approximates the area of theaperture to be covered. Such a condenser transmits a cone of light 1 5along the optical axis of the condenser which at the aperture plate hasa cross-section at least equal to the area of the lm aperture. In such asystem the maximum luminosity is along the optical axis of the condenseror along the principal rays passing through the center of the cone oflight and the center of the iilm aperture. Thus, in the image projectedupon the screen the maximum luminosity is in the center of the screenimage and the luminosity decreases from the center to the outer edges ofthe image.

'This variation of luminosity between the oenters and the edges of thescreen image is not objectionable where the picture is projected inblack-and-white and through a single aperture 80 only. However, thisvariation of luminosity becomes very objectionable where additive coloris used and especially where two or more pictures are projected insuper-imposed relationship upon the screen.

When two pictures are projected and a double aperture plate is used andthe two images projected therethrough are super-imposed to form acomposite image upon the screen. an entirely new technique ofillumination must be used. This 40 is due to the fact that where such asystem is used the dividing wall in the middle of the double apertureplate separates the plate into two film areas and where, for example,the double areas are vertically disposed, the bottom of the upper jpicture is projected at the bottom of the screen image, while the top ofthe lower picture is projected to the top of the screen image, althoughboth the bottom of the upper picture and the top of the lower pictureare in the center of the dou- 50 ble aperture and the area of greatestluminosity.

If the conventional type of condenser is used for such a purpose, thecone of light passing from the condenser must be spread to cover thearea of the double aperture plate. This spreading of I5 the light tocover the two apertures still leaves the center of the luminosity alongthe optical axis of the condenser, i. e., along the principal raypassing through the center ofthe cone ofl light and the center of the4double aperture plate. However, inthis system, the center ofthe-aperture plate no longer corresponds to the center of the screenimage, for inasmuch as the top and bottom image are super-imposed toform a composite image upon the screen, the bottom of the top nlm imageis projected at the bottom of the screen while the top of the bottomfilm image (which is also in the center of the aperture plate) isprojected at the top. of the screen image. Itwillbeseenthatforthisreasonthe center ofthe greatest luminositywhich isat the dividing wall of the aperture plate is not projectedto the centerof the screen image, but instead is projected to the top and to thebottom of the screen image. Similarly the areas o! lesser luminosity inthe top and bottom of the aperture plate are projected to the center o fthe screen image. Thus, instead of having-as where a'single aperture isused-a screen image with its greatest luminosity in the center andgradually diminishing luminosity to the edges of the picture, thegreatest luminosity is at the opposite edges of the screen and the pointof least luminosity is in its center. This variation in the luminosityof the screen image is extremely objectionable in an additive system ofcolor. Y

It must be remembered that one of the film images carries green colorvalues and is projected through a green filter, while lthe other fllmimage carries red color values and is projected through a red fllter.The color upon the screen image is created by the light passing throughthe color value images, thence through the filters and thence upon thescreen, and the more intense the light passing through the image orportions of the image, the more brilliant and intense is the color.

For this reason the conventional condenser system produces a compositeimage in which the central portion only is in naturalvcolor and on oneedge of which the red color predominates and is more brilliant, while onthe opposite edge a green color is predominant and more brilliant.'I'his gives to every such picture the eilectof having a red band ofcolor on one edge and a green band of color on the opposite, and greatlydetracts from the beauty and the naturalness of the picture. Thiscondition also tends to produce a color beat or pulsating of these twobands of predominate color atopposite. edges of the screen picture.

I have found that the only way in which this objectionable separation ofcolor or over-emphasis of color and beat can be eliminated is by sodesigning and constructing a condenser system that it will give an evenluminosity over the entire area of the double aperture plate and it isthe principal object of my invention to provide means for creating aneven distribution of light and an equal luminosity throughout both ofthe nlm areas defined by such double aperture plate. A further object isto provide a'novel construction of lens adapted for use in such acondenser system. The invention further comprises a novel method ofattaining an even distribution of light of equal intensity throughoutthe film areas dened by a double aperture plate for use in additivecolor projection.

The foregoing and other objects and advantages of the invention will bebetter understood from the following detailed description, and thedistinctive features of novelty will be thereafter pointed out in theappended claims.

Referring to the drawing:

Figure l is a diagrammatic view partly in ele' 5 vation and partly insection showing an apparatus embodying the invention;

Flgurezisadiagrammaticviewshowinga modified form of the invention; and

Figure 3 is a diagrammatic sectional view illustrating the manner ofproducing a-novel lens employed in my invention.

Il indicates a suitable light source from which' the light passesthrough an illuminating systemtotheiilmapertureathissystemcorrespondiugl to the usual condenser systembut constituted so astoilluminateallportionsofbothofthefilm apertureswith equal intensity. For his purpose the lens element Il of such systemcomprises two portions Ila and'llbas shown in Figure 3 so each of whichis composed of somewhat less than half of a complete lens. i. e., it isground away a small distance beyond its optical center lic. These lensportions are then united to form the composite lens element li. l2indicates a lens il element which cooperates with the lens element ll infocusing the light upon the adjacent film apertures l3a, Ilb oftheaperture plate I3.` I4 indicates a usual or suitable shutter systemwhich controls the passage of light to the film F which is operatedbetween the rolls R, R', and Il denotes a suitable lens system forfocusing the projected light upon a screen.

By reason of the special construction of the composite lens element Il,each of the two portions Ila, lib thereof directs a beam of light uponboth film apertures, and these beams indicated by the characters X, Y,cross at the locality of the nlm apertures or somewhat beyond the same.It is to be noted that each of the beams 40 X, Y a's directed by therespective lens portions lla, Hb is composed of rays which are directedin approximately parallel lines as they pass through lthe film aperturesand that each-of these beams covers the full extent of both apertures.45 From this it results that a substantially equal illumination of'allparts of both of the lm apertures I3a, I3b is eiected, and thus nodistortion will result from undue emphasis upon color values indiiferent portions of the respective film images. 50 In the form of theinvention shown in Figure 1 Y the lens element I2 which cooperates withthe element Il is shown as a simple plano-convex lens while in Figure 2a form is shown adapted for a different distance from the light source65 wherein the lens element I 2li which similarly cooperates with thelens element Il, is composed of two portions I2lla, |201, each of whichis ground away on one side, and then these portions united, these lensportions being not how- 6( ever ground away as far as the optical axesthereof.

I am aware that the invention may be embodied in other specific formswithout departing from the spirit or essential attributes thereof, and I6a therefore desire the present embodiment to be considered in allrespects as illustrative and not restrictive, reference being had to theappended claims rather than to the foregoing description to indicate thescope of the invention. 7

Having described my invention, what I claim is new and desire to secureby Letters Patent is:

l. Apparatus for double simultaneous projection comprising an apertureplate having two adjant film apertures, a light source, and means fordirecting light from such light source upon said lm apertures in twobeams with all portions of each beam in approximate parallelism and withthe beams superimposed one upon the other at the locality of the lmapertures, each of which covers substantially the full extent of bothapertures.

2. Apparatus for double simultaneous projection comprising an apertureplate having two adjacent lm apertures, a light source, and means fordirecting light from such light source upon said film apertures in twobeams with all portions of each beam in approximate parallelism and withthe beams superimposed one upon the other at the locality of the filmapertures, each 0f which covers substantially the full extent of bothapertures and which beams cross at the locality of such apertures.

3. Apparatus for double simultaneous projec tion comprising a lm platehaving two adjacent lm apertures, a light source, and means fordirecting light from such light source upon said apertures in two beams,each of which covers substantially the full extent of both apertures andwith all portions of each beam projected upon the apertures inapproximate parallelism.

4. Apparatus for double simultaneous projection comprising an apertureplate having two adjacent lm apertures, a light source, and means fordirecting light from said light source upon said apertures in two beamswith all portions said apertures in two beams with al1 portions l0 ofeach beam in substantial parallelism and each lighting the full area ofboth film apertures, embodying a lens element composed of two portionseach consisting of the remaining part of a plano-convex lens ground awaybeyond its optid- 15 cal center, each of such portions arranged todirect a beam of light upon substantially the entire extent of bothapertures and with the beams from the two portions crossing at thelocality of such apertures.

6. Apparatus as dened in claim 1 wherein the light directingmeans'embodies a composite'convex lens element for the purpose statedcomposed of two portions each ground away beyond its foptical center.

'7. Apparatus as defined in claim 1 wherein the light directing meansembodies a composite plano-convex lens element for the purpose statedcomposed of two lens portions each ground away beyond its optical centerthereof.

v RICHARD THOMAS.

